how to switch root and use exec function

[lucky2046]

The remote machine does not support root user SSH connection. Using test user SSH to connect to the remote machine to obtain session A, I can smoothly switch to root user through the session shell. Then, I execute whoami through the session exec command, prompting me that session A has been reused. How can I solve this problem?

[lucky2046]

package com.mixislink.task.ssh;

import lombok.extern.slf4j.Slf4j;
import net.schmizz.sshj.SSHClient;
import net.schmizz.sshj.common.IOUtils;
import net.schmizz.sshj.connection.channel.direct.Session;
import net.schmizz.sshj.transport.verification.PromiscuousVerifier;
import net.schmizz.sshj.userauth.UserAuthException;

import java.io.IOException;
import java.util.concurrent.TimeUnit;

@Slf4j
public class SSHTest {

    public static void main(String[] args) {
        String hostname = "192.168.100.185";
        int port = 22;
        String testUsername = "test";
        String testPassword = "123456";
        String rootUsername = "root";
        String rootPassword = "123456";

        try {
            SSHClient sshClient = new SSHClient();
            sshClient.addHostKeyVerifier(new PromiscuousVerifier()); // Use with caution, for testing purposes only

            // Connect with test user
            sshClient.connect(hostname, port);
            sshClient.authPassword(testUsername, testPassword);

            // Start an interactive session
            try (net.schmizz.sshj.connection.channel.direct.Session session = sshClient.startSession()) {
                // Start a shell
                session.allocateDefaultPTY();
                session.startShell();

                session.setAutoExpand(true);

                // Simulate the command to switch to root user
                session.getOutputStream().write(("su - root\n").getBytes());
                session.getOutputStream().flush();

                // Wait for a moment to allow the command to be executed and password to be prompted
                Thread.sleep(1000);

                // Provide the root password
                session.getOutputStream().write((rootPassword + "\n").getBytes());
                session.getOutputStream().flush();

                // Wait for a moment to allow the password to be validated
                Thread.sleep(1000);

                // Now, you are logged in as root. You can execute commands or perform any operations as root here.
                // For example, let's print the current user (should be root now)
                String command = "whoami";
                session.getOutputStream().write((command + "\n").getBytes());
                session.getOutputStream().flush();
                Thread.sleep(1000);

                // Read the command output
                byte[] buffer = new byte[1024];
                int read = session.getInputStream().read(buffer);
                String result = new String(buffer, 0, read);
                System.out.println("Current user: " + result.trim());

                Session.Command cmd = session.exec("whoami");
                System.out.println(IOUtils.readFully(cmd.getInputStream()).toString());
                cmd.join(5, TimeUnit.SECONDS);
                System.out.println("\n** exit status: " + cmd.getExitStatus());
                // Close the session when you're done.
                session.close();
            }

            // Don't forget to close the connection when you're done.
            sshClient.disconnect();

        } catch (UserAuthException e) {
            System.err.println("Authentication as test user failed. Make sure test user credentials are correct.");
        } catch (IOException | InterruptedException e) {
            e.printStackTrace();
        }
    }
}

[lucky2046]

i got error：
This session channel is all used up

if i use sshClient start new session，i got test，not root.

How can I solve this problem?

Session.Command cmd = sshClient.startSession().exec("whoami");
System.out.println(IOUtils.readFully(cmd.getInputStream()).toString());
 cmd.join(5, TimeUnit.SECONDS);